The present invention relates to a tungsten halogen lamp in which an infrared reflecting film is formed and to a method for manufacturing the same.
A single-end-sealed tungsten halogen lamp 17 as shown in FIG. 5 is known as a conventional tungsten halogen lamp (Japanese Patent Application No. (Tokkai Sho) 57-74963). In the tungsten halogen lamp 17, an infrared reflecting film 16 is formed on the surface of a straight-tube-shaped arc tube 15, in which a filament coil 14 is located, by alternately dipping the arc tube 15 in a solution for forming a TiO2 film and a solution for forming a SiO2 film.
In the conventional tungsten halogen lamp, gaps 18 that are not hermetically sealed occur between the quartz glass of a sealing portion 19 and metal foils 20 and outer leads 21, along parts of the metal foils 20 of molybdenum sealed in the sealing portion 19, and along the outer leads 21 having one end connected to the metal foils 20 and the other end led out of the sealing portion 19.
When the gaps 18 are present, air enters into the sealing portion 19 through the gaps 18, so that the metal foils 20 in the sealing portion 19 are oxidized during the lamp life. Therefore, leaks and cracks are eventually caused in the sealing portion 19, shortening the lamp life. In addition, the lamp efficiency of the tungsten halogen lamp increases only by about 7% by forming the infrared reflecting film 16.
Another conventional tungsten halogen lamp as shown in FIG. 6 is known (U.S. Pat. No. 5,045,748 and 5,138,219). The tungsten halogen lamp comprises a double-end-sealed elliptical arc tube 22 of fused quartz in an outer tube 24. An infrared reflecting film 23 is formed on the surface of the arc tube 22 by a CVD technique (chemical vapor deposition technique). With the CVD technique, the arc tube 22 is put into an evacuated furnace, and tantalum (Ta) and silicon (Si) atmospheres are created alternately in the furnace.
The luminous efficiency of this conventional tungsten halogen lamp increases by about 50% because of the infrared reflecting film 23 and the elliptical arc tube 22. However, since the tungsten halogen lamp has a double-tube structure in which the arc tube 22 is held in the outer tube 24, the structure is complicated and involves a high cost.
In order to solve the above problems, it is an object of the present invention to provide a tungsten halogen lamp that has a long life and a high efficiency and is inexpensive, and a method for manufacturing the same, by preventing the oxidation of the metal foils.
It is an object of the present invention to provide a tungsten halogen lamp comprising an arc tube of fused quartz having a sealing portion at one end with a halogen element and a rare gas enclosed and a filament coil held within the arc tube, an infrared reflecting film being formed on the surface of the arc tube, the sealing portion sealing metal foils connected to the filament coil and outer leads having one end connected to the metal foils and the other end led out of the sealing portion. The infrared reflecting film is formed on the surfaces of the outer leads and the surfaces of the metal foils, and at least a part of the surface of the sealing portion has a portion where the infrared reflecting film is not formed and/or a portion where at least a part of the infrared reflecting film is removed.
In the tungsten halogen lamp, the xe2x80x9cat least a partxe2x80x9d of the surface of the sealing portion refers to 20 to 100% of the surface of the sealing portion. The xe2x80x98at least a part ofxe2x80x99 the infrared reflecting film refers to 20 to 100% of the thickness of the formed infrared reflecting film.
It is preferable that the infrared reflecting film formed on the surface of the arc tube is a multilayer interference film in which layers of a high refractive material and layers of a low refractive material are alternately laminated and that the layer of a high refractive material is made of at least one material selected from the group consisting of Ta2O5, Nb2O5, CeO2, SiC, ZnS, TiO2, Si3N4, Y2O3, and ZrO2. Also, it is preferable that the layer of a low refractive material is made of at least one material selected from the group consisting of MgF2, SiO2, and Al2O3.
It is preferable that the total thickness of the infrared reflecting film formed on the surface of the arc tube is in the range of 0.8 to 3.5 xcexcm.
It is preferable that the thickness of the infrared reflecting film formed on the surfaces of the outer leads and the surfaces of the metal foils is in the range of 0.8 to 3.5 xcexcm.
It is preferable that at least a part of the arc tube has a swelling portion, and the filament coil is held on the central axis of the swelling portion.
It is preferable that the swelling portion has an elliptical shape.
The present invention provides a method for manufacturing a tungsten halogen lamp, the tungsten halogen lamp comprising an arc tube of fused quartz having a sealing portion at one end with a halogen element and a rare gas enclosed and a filament coil held within the arc tube, an infrared reflecting film being formed on the surface of the arc tube, the sealing portion sealing metal foils connected to the filament coil and outer leads having one end connected to the metal foils and the other end led out of the sealing portion. The method comprises the steps of forming the infrared reflecting film on the surface of the arc tube, the surfaces of the outer leads, the surfaces of the metal foils, and the surface of the sealing portion, and removing at least a part of the infrared reflecting film formed on the surface of the sealing portion.
In the method, it is preferable that the infrared reflecting film is formed by a chemical vapor deposition technique.
In the method, it is preferable that the infrared reflecting film is formed by dipping.
In the method, it is preferable that the infrared reflecting film formed on the surface of the sealing portion is removed by sand blasting.
According to the present invention, the temperature of the sealing portion can be decreased while the lamp is turned on. Furthermore, the outer leads and the metal foils exposed to the air in the gaps in the sealing portion can be shielded and protected from the oxygen in the air by the infrared reflecting film. Therefore, the oxidation of the metal foils can be avoided during the lamp life.
The present invention provides a method for manufacturing a tungsten halogen lamp, the tungsten halogen lamp comprising an arc tube of fused quartz having a sealing portion at one end with a halogen element and a rare gas enclosed and a filament coil held within the arc tube, an infrared reflecting film being formed on the surface of the arc tube, the sealing portion sealing metal foils connected to the filament coil and outer leads having one end connected to the metal foils and the other end led out of the sealing portion. The infrared reflecting film is formed on the surfaces of the outer leads and the surfaces of the metal foils exposed to gaps that are not hermetically sealed in the sealing portion, a portion where the infrared reflecting film is not formed being defined on the surface of the sealing portion. The method comprises the steps of forming the infrared reflecting film on the surface of the arc tube and removing the infrared reflecting film formed on the surface of the sealing portion.
Accordingly, a tungsten halogen lamp that can prevent the oxidation of the metal foils during the lamp life can be obtained.